A member of the immunoglobulin gene superfamily, SLAM is rapidly induced after activation of naive T- and B-cells. (Cocks, B. G., “A Novel Receptor Involved in T-Cell Activation,” Nature 376:260-263 (1995); Aversa, G., “Engagement of the Signaling Lymphocytic Activation Molecule (SLAM) on Activated T Cells Results in Il-2-Independent, Cyclosporin A-Sensitive T Cell Proliferation and IFN-gamma Production,” J. Immun. 4036-4044 (1997).) A multifunctional 70 kDa glycoprotein, SLAM causes proliferation and differentiation of immune cells. (Punnonen, J., “Soluble and Membrane-bound Forms of Signaling Lymphocytic Activation Molecule (SLAM) Induce Proliferation and Ig Synthesis by Activated Human B Lymphocytes,” J. Exp. Med. 185:993-1004 (1997).) To elicit an immune response, both a secreted form of SLAM, as well as a membrane bound SLAM, are thought to interact.
It is also known that dendritic cells (DC) are the principal antigen presenting cells involved in primary immune responses; their major function is to obtain antigen in tissues, migrate to lymphoid organs, and activate T cells. (Mohamadzadeh, M. et al., J. Immunol. 156: 3102-3106(1996).) In fact, DC are usually the first immune cells to arrive at sites of inflammation on mucous membranes. (See, e.g., Weissman, D. et al., J. Immunol. 155:4111-4117 (1995).) DC are also known to directly interact with B cells. There is a constant need to identify new polypeptide factors which may mediate interactions between DC and T cells and/or B cells, leading to the activation and/or proliferation of immune cells. To date, however, SLAM molecules have not been identified on DC cells.
Thus, there is a need for polypeptides that affect the proliferation, activation, survival, and/or differentiation of immune cells, such as T- and B-cells, since disturbances of such regulation may be involved in disorders relating to immune system. Therefore, there is a need for identification and characterization of such human polypeptides which can play a role in detecting, preventing, ameliorating or correcting such disorders.